Ok, that makes sense - got it.
This is where I'm at now.
Back end of the key mechanism - this looks flogged out to me and could be the cause of the issue?
View attachment 57222
Looking inside the barrel - this marries to the electrical part of the switch. This doesn't seem to have much wear on it.
View attachment 57223
Looking inside the barrel - this mates to the back of the key mechanism. Again this doesn't look too worn. That said I take your earlier point as the whole thing is gummed up with grease and old machine oil. Will degrease tomorrow.
What do you think the fix is here - new key mechanism?
View attachment 57224
ok, my opinion,
if there is nothing blocked or cracked or broken, cleaning is the solution
as far as i can see you have no plastic or teflon parts there
if you have access to compress air i woulddo the following,
get a contact cleaner spray (used in electronic to clean contacts leaves no residue and dries very quickly)
make a mixture 3/4 gasoline 1/4 diesel
get a glass full of mixture and put your bits inside
use a brush or similar to help the fluid cleaning tha outside and inside where you have access
replace fluid with clean one as needed
do the same with the key lock mechanism
let everything stirr a bit and blow compress air to help removing the mixture
the barrel will be happy with some wd40, apply in excess and let stirr over paper towels, do not remove the oil from surfaces, simply stirr
the key mechanism blow graphite powder through the key hole, and dip the key in graphite and insert the key, move it slowly backward and forwards, trying to spread the graphite internally, blow some graphite from the rear side too
make sure your key turns and works perfect
then clean the excess graphite
and use the oily wet paper towels to smear the external body of the key mech with a bit of oil to let it be inserted easily into the barrel, free the blocking tab and let oil hold there
try to avoid oil-graphite contact
my guess is that it will work great after that